1. Field of the Invention
The disclosure relates generally to a system and method for non-invasive analysis of material compositions using electromagnetic energy. More specifically, the disclosure relates to a system and method for non-invasive analysis of biological material and fluids therein.
2. Description of the Related Art
According to the National Diabetes Information Clearinghouse, in 2007, diabetes cost the United States $174 billion. Indirect costs, including disability payments, time lost from work, and reduced productivity, totalled $58 billion. Direct medical costs for diabetes care, including hospitalizations, medical care, and treatment supplies, amounted to $116 billion. Diabetes has no known cure, but may be managed with diet, exercise, and medication.
The ability for diabetics to self-monitor blood glucose has been a key advancement for control of the disease. There remains considerable research into “minimally invasive” and “non-invasive” methods for measuring blood sugar. Minimally invasive monitors require smaller blood samples than traditional invasive methods. These monitors measure blood taken from the finger or forearm. Samples from the forearm where nerves are not as close together as on the finger may be more comfortable for patients. The user pierces the skin, obtains a sufficient amount of blood, which is then placed on a test strip attached to a monitor that reports the glucose. Despite the advancements in minimal invasive sensors, there is a need for a truly non-invasive device that avoids the piercing of the skin for measuring glucose in a patient.
U.S. Pat. No. 5,077,476, Rosenthal, describes a near infrared (NIR) sensor which claims non-invasive measurement of glucose. The operation of the sensor involves introducing NIR energy into a body part and measuring a reflected signal via a receiving device in close proximity to the point of signal application. The received signal is analyzed to estimate blood glucose levels. NIR sensors have been studied for many years and a satisfactory non-invasive sensor has not been produced for the general market. The NIR signal has characteristic response that is sensitive to many tissue parameters and isolating a glucose specific response has been problematic.
The FDA has approved a glucose monitoring system for continuous use over twelve hours that is quasi non-invasive in the sense that penetration of the skin with a needle or lancet is not required. Instead, an electrical current draws glucose-containing fluid through the skin via reverse iontophoresis. This fluid is then analyzed for its glucose content. The device is not the non-invasive monitor diabetics seek. It lags behind traditional invasive methods by approximately 18 minutes, causes skin irritation in up to 50% of its users, and requires daily calibration by invasive glucose monitoring. The method is not a replacement for the traditional measurement; rather it is used only as a supplemental method between normal testing. Patents explaining this technology are shown, for example, in U.S. Pat. Nos. 6,144,869, 6,141,573, and 7,052,472.
Other needs for non-invasive fluid analysis in a patient, such as cholesterol, hormone levels, and the like, also involve invasive procedures. In a similar manner as the above issues with glucose, these levels can also benefit from non-invasive devices and methods.
It is well known that electromagnetic (“EM”) properties of most real world materials, including the complex electrical permittivity and the magnetic permeability, are frequency dependent. Permittivity is used to describe how an electric field affects and is affected by a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to an externally applied field and thereby reduce the total electric field inside the material. Permittivity is often expressed as a relative permittivity ∈r to the permittivity ∈0 of a vacuum. Thus, permittivity relates to a material's ability to transmit (or “permit”) an electric field. The response of real world materials to external fields normally depends on the frequency of the field, because the material's polarization does not respond instantaneously to an applied field. Permittivity for materials can be expressed as a complex function to allow specification of magnitude and phase of the permittivity as a function of the angular frequency (ω) of the applied field with real and imaginary components as follows:∈r(ω)=∈r′(ω)−j∈r″(ω)
Magnetic permeability, as another form of a material's response to applied EM energy, can be compared with electrical permittivity in that it is the degree of magnetization of material from reordered magnetic dipoles in the material when responding to a magnetic field applied to the material. Magnetic permeability is often expressed as a relative permeability to permeability in a vacuum. Magnetic permeability is frequency dependent for real world materials and can include real and imaginary components.
Thus, information concerning the composition of the substance can be obtained by exposing the substance to EM energy at different frequencies and analyzing the response at each frequency. Typically, the method for measuring the frequency-dependent characteristics of materials involves sequentially generating each frequency of interest or continuously varying over a range of frequencies that includes the frequency of interest, exposing the substance to energy generated at each frequency (also known as a “sweeping” or a swept frequency analysis), measuring at each frequency a property of the material, such as electrical permittivity or magnetic permeability, of the substance to the energy to which it is exposed, and then analyzing some aspect of the response of the material to determine the desired parameter value at each of those frequencies. Currently available industrial sensors and composition analyzers are used to obtain information concerning the composition of a substance to be processed by analyzing the response of the substance to electromagnetic energy.
U.S. Pat. No. 5,331,284, Jean, et. al., describes a meter and method marketed as a guided microwave spectrometer (GMS) system that uses a different approach for obtaining frequency dependent information. In the GMS system, a broad-band measurement is performed by stepping sequentially through a range of frequencies (“sweeping”) and measuring the transmission cutoff characteristics of a waveguide that contains the material under test. By analyzing this spectral response of the waveguide, the effects of the frequency-dependent electrical properties can be calibrated to yield multi-component analysis of various mixtures.
U.S. Pat. No. 6,987,393, Jean et al., describes use of ultra-wide band (UWB) pulse technology for the measurement of the frequency response of industrial measurement cells and pipes containing an unknown material whose electrical properties are to be measured. UWB pulse technology is used to provide a sequence of electromagnetic (EM) energy pulses of relatively short duration to generate a very broad frequency band of energy. These pulses are communicated to the substance to be analyzed. The response of the substance to the pulses is measured and analyzed to determine properties of the substance. Knowledge of the properties of the substance may then be usefully employed in an industrial or other process involving the substance. The substance interacting with the pulsed energy provided will produce dispersion of the pulses. This dispersion is a function of the characteristics of the substance and affects the shape, duration, phase, and time of arrival of the energy pulses coupled to a sampling pulse receiver. A response signal arising from interaction of the substance with the pulse of energy can be transformed with a Fourier mathematical transform to produce a signal indicative of a response of the substance to energy at different frequencies within the range of frequencies in the spectrum of the pulsed signal.
Despite the progress in this field for non-invasive analysis, substantial needs remain. For example, it has been noted that a general characteristic frequency curve of biological materials exposed to EM energy forms a generally cascading downward curve having multiple regions, where the frequency is the X-axis and the complex permittivity is the Y-axis. One example of this research is seen in “Permittivity of Human Skin in the Millimeter Wave Band” C. M. Alabaster, IEE Electronics Letters, Vol. 39, No. 21, 16 Oct. 2003, pp. 1521-2. The curve is defined by the property(ies) of the material being measured. No known instrument can be used to field test such multiple regions for general public use that is economically and commercially viable. Thus, the asserted usefulness of the study's underlying technology does not provide the acclaimed benefits to those who need it the most.
There remains a need for an improved system and method for non-invasive analysis of biological materials and fluids therein.